This two-stage, multi-center, randomized, controlled, open-label study will investigate the pharmacokinetics, efficacy and safety of rituximab SC versus rituximab IV in participants with previously untreated follicular non-Hodgkin's lymphoma. Participants will be randomized to receive 375 milligrams per meter square (mg/m\^2) rituximab as IV infusion or 1400 milligrams (mg) rituximab SC. In addition, participants will receive standard chemotherapy. Participants who achieved a complete or partial response (PR) after 8 treatment cycles, will receive maintenance treatment for a further maximum number of 12 cycles. Maintenance treatment cycles will be repeated every 8 weeks. This is a two-stage study. Stage 1 was designed to confirm the chosen rituximab SC dose resulting in comparable rituximab serum Ctrough levels compared with rituximab IV, when given as part of induction treatment every 3 weeks. Enrollment for Stage 2 started after the rituximab SC dose was established in Stage 1. Stage 2 aimed to further investigate the efficacy and safety of rituximab SC compared with rituximab IV. The anticipated time on study treatment is 96 weeks.